When soft tissue tears away from bone, reattachment becomes necessary. Various devices, including sutures alone, screws, staples, wedges, and plugs have been used in the prior art to secure soft tissue to bone.
Recently, various types of threaded suture anchors have been developed for this purpose. Some threaded suture anchors are designed to be inserted into a pre-drilled hole. Other suture anchors are self-tapping.
U.S. Pat. No. 4,632,100 discloses a cylindrical threaded suture anchor. The suture anchor of the '100 patent includes a drill bit at a leading end for boring a hole in a bone, followed by a flight of threads spaced from the drill bit for securing the anchor into the hole created by the drill bit.
U.S. Pat. No. 5,370,662 discloses a suture anchor having threads which extend to the tip of the anchor. U.S. Pat. No. 5,156,616 discloses a similar suture anchor having an axial opening for holding a knotted piece of suture.
All of the above-noted suture anchors include a structure for attaching the suture to the anchor. U.S. Pat. No. 4,632,100, for example, discloses a press-fitted disc and knot structure which secures the suture to the anchor. In other suture anchors, such as those disclosed in U.S. Pat. No. 5,370,662, the suture is passed through an eyelet located on the proximal end of the anchor. In the case of a bioabsorbable suture anchor, the suture may be insert molded into the anchor, as disclosed in U.S. Pat. No. 5,964,783.
Problems can arise if the structure for attaching the suture fails, allowing the suture to become detached from the anchor. Also, the suture often is exposed to abrasion or cutting by sharp or rough areas along the walls of the bone canal into which the anchor is inserted.
Moreover, the eyelet or, in the case of U.S. Pat. No. 4,632,100, the axial opening for receiving the disc to which the suture is knotted, is formed as part of the drive head of the known suture anchors. Combining these two functions in one structure often tends to weaken the drive head.
In addition, various other modifications to the drive head often are employed in connection with suture attachment. For example, recessed grooves may be formed on opposite sides of the drive head to receive and protect the suture from abrasive areas of the suture anchor tunnel or to facilitate mating between the anchor to the driver. In such cases, the drive head often must be made of a larger diameter to recover the mechanical strength lost from the removal of material relating to the suture-attachment or suture-protection modifications.
Further, the prior art suture anchors having eyelets extending from the proximal ends require countersinking of the eyelet below the bone surface to avoid having the patient's tissue abrade against the exposed eyelet. As a result, suture attached to the eyelet is vulnerable to abrasion by the bony rim of the countersunk hole into which the suture anchor is installed. In addition, in biodegradable suture anchors, the suture eyelet can degrade rapidly, causing the suture to become detached from the anchor prematurely.
Accordingly, there is a need for a threaded suture anchor to which suture is secured effectively so as to prevent detachment of the suture. It is further desirable for such suture anchors to have eyelets that will not abrade tissue and which do not require countersinking.
Further, there is a need for a suture eyelet shield within a biodegradable suture anchor with a bearing surface that will resist suture cut-through of the bioabsorbable material.